The present invention generally relates to a light regulator for adjusting the amount of light passing therethrough and, more particularly, to an electro-optical regulator utilizing the phenomenon of electrochromism for regulating the amount of light passing therethrough.
The U.S. Pat. No. 3,476,029, patented on Nov. 4, 1969, discloses the use of an electrochromic cell as a shutter mechanism or a diaphragm mechanism, or a combination thereof, for a photographic camera. The electrochromic cell disclosed in the above numbered U.S. patent comprises an electrochromic material normally opaque to light placed between transparent plates each bearing a transparent electrode arrangement on its inner surface. The respective electrode arrangement employed in the electrochromic cell referred to above is constituted by either a central transparent electrode and a plurality of ring-shaped transparent electrodes arranged coaxially with the central electrode and positioned in a coaxially spaced relation to each other or by a plurality of substantially rectangular transparent electrodes arranged in a spaced parallel relation to each other. This cell is so designed that, when an electric potential is applied between pairs of the electrodes on the respective transparent plates, the electrochromic material sandwiched between the pairs of the electrically energized electrodes becomes transparent so that light can pass completely through the electrochromic cell.
However, the three types of electrochromic light regulators shown respectively in FIGS. 1 and 2, FIG. 3 and FIG. 4 of the accompanying drawings are well known to those skilled in the art. The electrochromic light regulator having the construction shown in FIGS. 1 and 2 and generally identified by 10 comprises a transparent substrate 11 having one surface covered with a common transparent electrode 12, made of an electroconductive material such as SnO.sub.2 or In.sub.2 O.sub.3 and formed by the use of a known etching technique or a known metal vapor bonding technique, and an electrochromic layer 13 overlaying the common electrode 12 and made of a transition metal oxide such as WO.sub.3 or MoO.sub.3. The electrochromic light regulator further comprises a transparent central electrode 14 having a substantially disc-like shape, and a plurality of, for example three, substantially annular transparent electrodes 15, 16 and 17 coaxially encircling the central electrode 14 and one encircling the other in a spaced manner, all of these electrodes 14 to 17 lying in one and the same plane, and an ion conducting and electrically insulating layer 18 made of a material such as SiO, SiO.sub.2 or MgF.sub.2 and positioned between the electrochromic layer 13 and the electrodes 14 to 17.
The electrochromic light regulator having the construction shown in FIG. 3 is similar to that shown in FIG. 1 and 2, except that the common electrode 12 and the central and annular electrodes 14 to 17 are reversed in position.
In both types of the electrochromic light regulators shown respectively in FIGS. 1 and 2 and in FIG. 3, as best shown in FIG. 1, each of the annular electrodes 15 to 17 in reality has a split-ring shape and has, therefore, a gap between its opposed ends. For the purpose of external electric connection, each of the annular electrodes 15 to 17 has a lead-out conductive strip 15a, 16a or 17a extending radially outward from one of the opposed ends thereof. Similarly, the central electrode 14 having a substantially circular shape has a lead-out conductive strip 14a extending radially outward therefrom in spaced and parallel relation to the conductive strips 15a, 16a and 17a and terminating at a position outside of the outermost annular electrode 17 after having passed through the respective gaps between the opposed ends of the annular eletrodes 15 to 17.
In this construction, when an electric voltage is applied between the common electrode 12 and one or more of the annular electrodes 15 to 17, the portion or portions of electrochromic layer 13 located between the common electrode 12 and such one or more of the annular electrodes 15 to 17 becomes colored and, in particular, the portion or portions of electrochromic layer 13 corresponding to the location of such one or more of the electrodes 15 to 17 becomes colored in a split-ring configuration, leaving an uncolored area between the opposed ends of the annular electrodes. By way of example, if an electric voltage is applied between terminals E and Z, the portion of electrochromic layer 13 corresponding to the location of the annular electrode 17 becomes colored. In this condition, the gap between the opposed ends of the annular electrode 17 through which the lead-out conductive strips 14a, 15a and 16a from the associated electrodes 14 to 16 extend remains uncolored. This is not only uncomfortable for a person to look upon, but also provides an uneven performance in light control in that the portion of the light passing through the gap between the opposed ends of the electrodes, which remains uncolored, cannot be intercepted.
Moreover, in view of the fact that not only does each of the annular electrodes 15 to 17 have a potential gradient, but also the resistance between each of the electrodes 15 to 17 and the common electrode 12 is very high, coloration of the electrochromic layer 13 when activated by the applied voltage starts from a portion corresponding to the lead-out conductive strip 15a, 16a or 17a where the voltage is first applied, and progresses towards the portion corresponding to the opposed end of such annular electrode remote from the lead-out conductive strip 15a, 16a or 17a. This means that a time is required for the portion of electrochromic layer 13 corresponding to the annular electrode to complete its coloration over its entire length. This process of coloration at first results in variation in optical density between the opposed end portions of the same electrode. In order for the portion of electrochromic layer 13 corresponding the same electrode to be completely colored, the conventional light regulator requires a relatively large electric potential be supplied, which in turn prevents the use of a relatively low, and therefore economical, drive voltage for driving the light regulator.
However, the disadvantages of slow response, variation in optical density and the incapability of using a low drive voltage, inherent in the light regulator having the construction shown in either FIGS. 1 and 2 or FIG. 3 can be substantially eliminated by providing additional lead-out conductive strips, such as shown by 15b, 16b and 17b in FIG. 4, in the respective ends of the annular electrodes 15 to 17 remote from the lead-out conductive strips 15a, 16a and 17a. However, even in the contemplated arrangement shown in FIG. 4, there is still a disadvantage in that the light passing through one or more gaps between the opposed ends of the electrically activated annular electrodes cannot be intercepted as is the case with the conventional light regulator of the construction shown in either FIGS. 1 and or 2 and FIG. 3.
Furthermore, where a relatively high contrast is required between the colored and uncolored portions of the electrochromic layer, the conventional light regulator cannot produce a contrast value higher than that attained when the coloration of the colored portion is saturated to the maximum optical density.